feat(examples): updates to hello-world example and directory reorganization

[campionfellin]

We want more examples (as per #22) but we should improve the current examples first so they work out of the box (git clone straight to example).

🎉First PR 🎉

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[campionfellin]

Looks like the yarn build from Lerna is failing because the build script in the example doesn't do the generate first.

Do we want:

1. Lerna to ignore the /examples
2. Examples to contain the cdk8s generate in build script?

I'd lean more towards 1, as I don't think cdk8s generate is needed for every build.

[eladb]

@campionfellin I think we should reorganize examples such that each example is a separate project (like yours) and change lerna and yarn from looking under examples to examples/* (should be both in package.json and lerna.json).